Network Working Group C. Allocchio
Request for Comments: 2304 GARR-Italy
Category: Standards Track March 1998
Minimal FAX address format in Internet Mail
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
IESG NOTE
This memo describes a simple method of encoding PSTN addresses of
facsimile devices in the local-part of Internet email addresses.
As with all Internet mail addresses, the left-hand-side (local- part)
of an address generated according to this specification, is not to be
interpreted except by the MTA that is named on the right-hand-side
(domain).
1. Introduction
Since the very first e-mail to fax gateway objects appeared, a number
of different methods to specify a fax address as an e-mail address
have been used by implementors. Two major objectives for this were
- enable an e-mail user to send faxes from his/her e-mail
interface;
- enable some kind of "fax over e-mail service" transport, to
reduce the costs of fax transmissions, and use the existing
e-mail infrastructure.
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RFC 2304 Minimal FAX address format March 1998
This memo describes the MINIMAL addressing method and standard
extensions to encode FAX addresses in e-mail addresses, as required
in reference [13]. The opposite problem, i.e. to allow a traditional
numeric-only fax device user to access the e-mail transport service,
is not discussed here.
All implementations supporting this FAX over e-mail address format
MUST support as a minimum the specification described in this
document. The generic complex case of converting the whole PSTN
addressing in e-mail is out of scope in this minimal specification:
there is some work in progress in the field, where also a number of
standard optional extensions are being defined.
In this document the formal definitions are described using ABNF
syntax, as defined into [7]. We will also use some of the "CORE
DEFINITIONS" defined in "APPENDIX A - CORE" of that document. The
exact meaning of the capitalised words
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", "OPTIONAL"
is defined in reference [6].
2. Minimal Fax address
The "service-selector" defined in section 2 of reference [13] for the
fax service is:
service-selector = "FAX"
The minimal addressing for the fax service also requires support for
a "qualif-type1" element (see section 2 of reference [13]). This
element is an OPTIONAL element of the fax address, but its support,
when present, is REQUIRED:
qualif-type1 = "/" t33-sep "=" sub-addr
where
t33-sep = "T33S"
sub-addr = 1*( DIGIT )
Thus, the minimal specification of a fax in e-mail address is:
fax-address = fax-mbox [ "/T33S=" sub-addr ]
fax-mbox = "FAX=" global-phone
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RFC 2304 Minimal FAX address format March 1998
Note:
See section 4.1 in case multiple sub-addr per fax-mbox need to be
specified.
The Minimal supported syntax for global-phone (as described in
section reference [13]) is:
global-phone = "+" 1*( DIGIT , written-sep )
written-sep = ( "-" / "." )
The use of other dialling schemas for PSTN numbers (like private
numbering plans or local dialling conventions) is also allowed.
However, this does not preclude nor remove the minimal compulsory
requirement to support the "global-phone" syntax as defined above.
Any non "global-phone" dialling schema MUST NOT use the leading "+"
between the "=" sign and the dialling string. The "+" sign is
strictly reserved for the standard "global-phone" syntax.
Note:
The specification of these different dialling schemas is out of
scope for this minimal specification.
User specification of PSTN e-mail addresses will be facilitated if
they can insert these separators between dial elements like digits
etc. For this reason we allow them in the syntax the written-sep
element.
Implementors' note:
Use of the written-sep elements is allowed, but not recommended.
Any occurences of written-sep elements in a pstn-mbox MUST be
ignored by all conformant implementations. User Agents SHOULD
remove written-sep elements before submitting messages to the
Message Transport System.
2.2 Some examples of a minimal "fax-address"
FAX=+3940226338
FAX=+12027653000/T33S=1387
FAX=+33-1-88335215
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RFC 2304 Minimal FAX address format March 19983. The e-mail address of the I-fax device: mta-I-fax
An "I-fax device" has an e-mail address, or to be more exact, a name
which enables a mail system to identify it on the e-mail global
system.
In Internet mail, this is the Right Hand Side (RHS) part of the
address, i.e. the part on the right of the "@" sign. We will call
this mta-I-fax
mta-I-fax = domain
For "domain" strings used in SMTP transmissions, the string MUST
conform to the requirements of that standard's <domain>
specifications [1], [3]. For "domain" strings used in message
content headers, the string MUST conform to the requirements of the
relevant standards [2], [3].
Note: in both cases, the standards permit use of "domain names" or
"domain literals" in addresses.
4. The fax-email
The complete structure used to transfer a minimal FAX address over
the Internet e-mail transport system is called "fax-email". This
object is an e-mail address which conforms to RFC822 [2] and RFC1123
[3] "addr-spec" syntax, with some extra structure which allows the
FAX number to be identified.
fax-email = ["/"] fax-address ["/"] "@" mta-I-fax
Implementors' note:
The optional "/" characters can result from other mail transport
services gateways, where it is also an optional element.
Implementations MUST accept the optional slashes but SHOULD NOT
generate them. Gateways are allowed to strip them off when
converting to Internet mail addressing.
It is essential to remind that "fax-address" element MUST strictly
follow the "quoting rules" spcified in the relevant standards [2],
[3]
4.1 Multiple subaddresses
In case a particular service requires multiple T.33 subaddresses, and
these subaddresses need to be given on the same "fax-mbox", multiple
"fax-email" elements will be used.
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RFC 2304 Minimal FAX address format March 1998
Implementors' note:
The UA could accept multiple subaddress elements for the same
global-phone, but it must generate multiple "fax-mbox" elements
when passing the message to the MTA.
4.2 Some examples of minimal "fax-email"
FAX=+3940226338@faxworld.org
FAX=+12027653000/T33S=1387@faxworld.org
/FAX=+33-1-88335215/@faxworld.org
5. Conclusion
This proposal creates a minimal standard encoding for FAX addresses
within the global e-mail transport system. The proposal requires no
changes to existing e-mail software.
6. Security Considerations
This document specifies a means by which FAX addresses can be encoded
into e-mail addresses. As routing of e-mail messages is determined by
Domain Name System (DNS) information, a successful attack on this
service could force the mail path via some particular gateway or
message transfer agent where mail security can be affected by
compromised software.
There are several means by which an attacker might be able to deliver
incorrect mail routing information to a client. These include: (a)
compromise of a DNS server, (b) generating a counterfeit response to
a client's DNS query, (c) returning incorrect "additional
information" in response to an unrelated query. Clients SHOULD ensure
that mail routing is based only on authoritative answers. Once DNS
Security mechanisms [5] become more widely deployed, clients SHOULD
employ those mechanisms to verify the authenticity and integrity of
mail routing records.
7. Author's Address
Claudio Allocchio
Sincrotrone Trieste
SS 14 Km 163.5 Basovizza
I 34012 Trieste
Italy
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RFC 2304 Minimal FAX address format March 19989. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
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